Surgical valved conduits or grafts, including a prosthetic vascular conduit with an associated prosthetic valve to control flow of blood through the conduit, may be used for various purposes including, for example, the replacement of the aortic valve in conjunction with the ascending aorta. The aorta is the largest blood vessel in the human body, carrying blood from the left ventricle of the heart throughout the body. The ascending aorta is the first section of the aorta, which stems from the left ventricle and extends to the aortic arch. The aortic valve is located at the root of the ascending aorta and controls the blood flow by permitting blood to flow from the left ventricle into the ascending aorta while preventing or restricting blood flow in the opposite direction.
In the so-called Bentall procedure, the combined pathologies of ascending aorta and aortic valve are replaced. There are a number of combined conduits and valves on the market. Prior bioprosthetic valved conduits, as with bioprosthetic heart valves, are stored in a liquid preserving or preservative solution, and thus the conduits are formed of woven polyester without a bioresorbable sealant. Although such conduits are suitable in certain situations, and tend to seal relatively quickly to the body from tissue ingrowth, too much blood can initially seep through their walls after implantation, which may be detrimental. Uncoated fabric such as polyethylene terephthalate (PET) has a high leakage rate, and thus the surgeon needs to pre-clot the graft with patient's blood before use. Others have proposed using a non-bioresorbable sealant layer, such as silicone, for example, as described in U.S. Patent Publication No. 2008/0147171 to Ashton, et al., published Jun. 19, 2008, but such layered conduits tend to be relatively thick-walled and not very flexible, and so are not preferred. For example, BioValsalva™ porcine aortic-valved conduits (Vascutek, Renfrewshire, Scotland, UK) include either three layers with an inner woven polyester, central elastomeric membrane, and outer ePTFE wrap, or two layers without the outer ePTFE layer. Nevertheless, such grafts still produce unacceptable leaking.
Consequently, some surgeons prefer conduits or grafts in which porous tubular structures, such as woven polyester (e.g., DACRON® polyethylene terephthalate (PET), Invista, Wichita, Kans.), are impregnated with bioresorbable materials such as gelatin, collagen, or albumin. For instance, Gelweave Valsalva™ Grafts (Vascutek, Renfrewshire, Scotland, UK) are gelatin sealed, aortic root grafts indicated for aortic root replacement. These conduits are not porous initially, and thus prevent blood loss, but the sealant medium eventually degrades by hydrolysis when exposed to water after implantation and is replaced by natural tissue ingrowth. Gelatin in the graft can also be treated in such a way as to cause cross-linking between amine groups in the gelatin molecules, rendering the gelatin more resistant to hydrolysis.
Conduits or grafts sealed using bioresorbable materials that include bioprosthetic heart valves are not pre-assembled because the liquid sterilant in which tissue valves are stored will eventually wash the bioresorbable sealing medium (gelatin, collagen, albumin, etc.) out of the permeable conduit material. Because of the benefits of using sealed conduits or grafts and because of the positive attributes of bioprosthetic heart valves, surgeons couple the two components together at the time of surgery, post-storage. Recently, so-called dry tissue heart valves have been developed, for example, described in U.S. Pat. No. 7,972,376 (Dove, et al.), in which bioprosthetic heart valves are pretreated with an aldehyde-capping agent prior to dehydration and sterilization. U.S. Patent Application Publication No. 2013/0325111 A1 to Campbell, et al. discloses a valved conduit that utilizes such a dry tissue valve connected within a tubular conduit sealed with a bioresorbable material. The Campbell valved conduit may be stored dry in a pre-assembled state, thus eliminating the time-consuming process of securing the two components together in the operating theater.
There remains a need for improved manufacturing techniques for valved conduits that ensure long term viability and efficacy, in particular in ensuring that the valved conduits will not leak excessively.